Method and apparatus for maintaining a constant image amplitude in a resonant mirror system

Abstract

A method for maintaining the amplitude of oscillations of a mirror system comprising a high-Q resonant mirror driven by a high speed drive signal. Sensors monitor the sweep amplitude of the high-Q resonant mirror and a parameter of the drive signal is adjusted to maintain the sweep amplitude of the mirror at a constant value. According to one embodiment, the frequency of the drive signal is adjusted to more closely track the resonant frequency of the mirror, and according to another embodiment, the amplitude of the drive signal is increased to increase the amplitude of the sweep motion of the mirror. According to a third embodiment, the sweep amplitude may be maintained by adjusting both the drive signal amplitude and the drive signal frequency.

1 . In systems comprising a high-Q resonant mirror for generating scan lines a method of maintaining a constant amplitude of mirror oscillations comprising the steps of: 
 providing a high frequency signal for driving said high-Q resonant mirror with a selected amplitude and having a central frequency substantially at the resonant frequency of said mirror;    providing sensors to monitor the amplitude of said resonant mirror; and    adjusting a parameter of said high frequency drive signal to maintain the amplitude of said high-Q resonant mirror substantially at said selected amplitude.    
   
   
       2 . The method of  claim 1  wherein said step of adjusting the parameter of said high frequency drive signal comprises adjusting the amplitude of said high frequency drive signal.  
   
   
       3 . The method of  claim 1  wherein said high frequency drive signal is a sinusoidal signal.  
   
   
       4 . The method of  claim 1  wherein said step of adjusting the parameter of said high frequency drive signal comprises adjusting the frequency of said high frequency signal.  
   
   
       5 . The method of  claim 4  further comprising adjusting the amplitude of said high frequency signal at the same time the frequency of said high frequency signal is being adjusted.  
   
   
       6 . The method of  claim 3  further comprising a low frequency mirror for positioning said scan lines.  
   
   
       7 . The method of  claim 6  wherein said low frequency mirror is driven by the sinusoidal signal.  
   
   
       8 . The method of  claim 6  wherein said signal driving said high frequency mirror is about a 20 kHz signal and said signal driving said low frequency mirror is about a 60 Hz signal.  
   
   
       9 . The method of  claim 1  wherein said step of maintaining the amplitude of said high frequency mirror constant comprises the steps of: 
 temporarily changing the frequency of said high frequency drive signal by a selected amount in a first direction to a new selected frequency;    monitoring the amplitude change of said high speed mirror drive due to said temporary frequency change in said first direction;    if said amplitude of said mirror increases, adjust the central frequency of said high speed drive signal to said new selected frequency; and    if said amplitude of said mirror decreases, temporarily change the frequency of said high speed mirror by said selected amount in the opposite direction and repeat said step of monitoring the amplitude change and adjusting the frequency.    
   
   
       10 . The method of  claim 1  wherein said system is a laser printer.  
   
   
       11 . The method of  claim 1  wherein said system is a visual display.  
   
   
       12 . The method of  claim 1  wherein said step of adjusting is continuous.  
   
   
       13 . The method of  claim 7  wherein said low frequency drive signals define peak portions and display portions, and said step of adjusting occurs during said peak portions.  
   
   
       14 . The method of  claim 13  wherein said step of adjusting occurs during both said peak portions and said display portion.  
   
   
       15 . The method of  claim 7  wherein said low frequency drive signals define peak portions and forward moving and reverse moving display portions.  
   
   
       16 . The method of  claim 15  wherein said scan lines are generated in both said forward and reverse moving display portions.  
   
   
       17 . The method of  claim 15  wherein said scan lines are generated in only one of said forward and reverse moving display portions, and said step of adjusting occurs during the other one of said forward and reverse moving display portions.  
   
   
       18 . The method of  claim 1  wherein said high-Q resonant mirror is further supported by a gimbals portion and a second set of torsional hinges and wherein movement about said second set of torsional hinges positions said scan line on a display surface orthogonally to the sweep of said scan lines.  
   
   
       19 . The method of  claim 10  wherein said step of adjustment occurs between pages being printed.  
   
   
       20 . The method of  claim 6  wherein said low frequency mirror reflects light toward said scanning mirror.  
   
   
       21 . The method of  claim 6  wherein said high frequency resonant mirror reflects light toward said slow speed positioning mirror.